Sheets for household use are well known in the art. It is often desired to decorate such sheets, such as by printing. Printing imparts an aesthetically pleasing pattern to the sheet. Alternatively, the sheet may be embossed to impart an aesthetically pleasing pattern which is also tactually discernible.
Such sheets are typically made in continuous form, then later cut to discrete lengths as desired. Such cutting to discrete lengths may occur at the point of use, such as is caused by the consumer detaching one sheet from the balance thereof at a line of termination. For this purpose, the line of termination typically comprises a line of weakness, such as a perforation. Alternatively, the continuous sheet may be folded and cut into discrete portions prior to the point of use. Such an arrangement often occurs in individual napkins which are folded and cut during manufacture and purchased by the consumer as discrete units.
It has been relatively facile in the prior art to register indicia with the cross machine direction of such sheets while such sheets are transported in a continuous fashion during a converting operation. However, it is more difficult to register the indicia in the machine direction, and particularly difficult to register the indicia with lines of termination, perforations, or folds produced by the converting machinery.
A phasing device is necessary to ensure that a machine direction misalignment of the web caused by web slippage or stretching will not cause each of the indicia occurring after the slippage or stretching to be placed out of registry with the converting machinery. Significant misregistry between the web indicia and converting machinery results in scrap of succeeding portions of the web affected by the misregistry. Therefore, an accurate web phasing device is essential for any commercial high speed converting operation requiring indicia to be registered in the machine direction relative to the operation being performed.
To control phasing of the web indicia with a particular converting operation it is necessary to monitor the degree of registry of the indicia with the converting operation in order to make the necessary adjustments in the converting operation machinery. Such monitoring device is generally performed by a photoelectric scanning device, generally referred to in the industry as a photo eye unit which senses registration marks on the web associated with each indicia and generates an indicia reference signal. In an ideal situation, the photo eye unit would be positioned within the operating station and would sense a registration mark at exactly the time that the associated converting operation were being performed on the web. A reference signal generated by the converting operation would be input to a signal comparator along with the web indicia signal to determine the degree of misregistry between the web and the equipment performing the converting operation. The system would then compensate for the misregistry by adjusting the orientation of the converting equipment. However, it is often times physically impossible to locate a photo eye unit in proximity to the converting equipment capable of detecting a registration mark located on the same region of the web in which the operation is being performed.
The placement of the photo eye away from the converting operation performed on the web is addressed in U.S. Pat. No. 5,802,974 issued to McNeil Sep. 8, 1998 the disclosure of which is incorporated herein by reference. McNeil addresses registering decorative indicia printed on a web moving in the machine direction with web perforations aligned in the cross machine direction. A photo eye detects misregistration via a signal comparator and adjust either the printing operation or the perforating operation while the web speed remains constant.
Varying the speed of an in-line operation such as perforating or printing can be accomplished where the web speed is maintained by a set of nip rollers or a winding operation which pulls the web past the operation being performed. During folding operations, folding cylinders are typically the last operation in the process such that adjusting the rotation of the folding cylinders to maintain print registration requires concurrent adjustment in the web speed. Although the design may be feasible, the maintenance of such a complex system may render it impractical, particularly for high speed applications.
For the present invention, a sensor for detecting misregistration of the indicia is placed a set distance upstream of the folding operation with a set of nip rolls interposed therebetween for controlling the speed of the web. A web speed control varies the rotational speed of the nip rolls increasing or decreasing the web speed to synchronize the registration of the indicia with fold lines produced by folding cylinders.